A superconductor wire is used in the energy field, such as power generation, power transmission and power supply, or in the field of traffic transport, such as a train raised above a surface by the magnetic effect (linear motor car), or in other fields.
Recently oxide superconductors which operate at temperature higher than the temperature of liquid nitrogen (77K) have been invented, and the possible fields in which the superconductors may be applied are expanding rapidly. The development of superconducting wire technology is required in order to place the superconductor technology into practical use.
A well-known conventional wire making process for production of superconductor wire as follows; on organic bonding agent and a superconductor oxide powder are mixed, then the mixture is placed in a metal pipe composed of Cu--Ni or Ag, and the mixture is formed into a wire by swaging etc. The pipe is then removed, and the product is heat-treated (BULLETIN OF THE JAPAN INSTITUTE OF METALS, VOL. 26 NO. 10 1987, page 980). According to this process, in the heat treatment process, the bonding agent is vaporized, and at the same time the superconductor oxide powder is sintered with large volume shrinkage to provide the sintered wire.
Additionally, another process is as follows; the superconductor oxide powder is pressed into a copper container by about 500 kg/cm.sup.2 pressure, is pre-heated for about 5 minutes in an electric furnace, and is then immediately put into an anti-pressure container and extruded by a press (JOURNAL OF THE JAPAN SOCIETY OF POWDER AND POWDER METALLURGY, VOL. 34 NO. 10, December 1987, page 117). According to this process, after the extrusion, a heat-treatment is carried out in order to obtain the superconductor property.
However, the sintered wire produced by the first process composed of only the superconductor oxide powder is very brittle and is cracked by external force and impact.
On the other hand, in second process, the circumference of the wire is covered with metal, so that the superconductor has good mechanical strength, but the production requires several separate extrusion steps. Namely, several extrusion steps are required because of the flow property of the superconductor oxide powder at high temperature. It is not possible to enlarge the squeezing ratio of the copper container filled with the superconductor powder. Additionally, at high temperature the amount of extrusion of the copper container filled with the oxide superconductor is limited, so that a long wire cannot be produced.